In humans, the survival of the young is dependent to a significant degree on the exertions of the mother, and the quality of her care will contribute to the foundation of the infant’s neurobiological, cognitive and socio-emotional development (Shonkoff et al., 2012). Furthermore, almost every women will experience pregnancy which is recognized to predispose the mother to a period of mental vulnerability (Brunton and Russell, 2008). Nevertheless, very little is known on how pregnancy affects the human brain.
It has been proven that less extreme endocrine changes render morphological brain modifications (Erickson et al., 2010; Woolley and McEwen, 1993, 1992) and several studies in mammals show adaptations in various brain systems in order to ensure pregnancy, delivery and postnatal care, suggesting in humans a brain plasticity inherent to reproduction itself (Brunton and Russell, 2008; Kinsley and Amory-Meyer, 2011; Swain et al., 2014). Although this question has been previously addressed assessing whole brain changes in size (Oatridge et al., 2002), the current findings are the first to explicitly show the precise morphologic brain changes associated with successful reproduction in human mothers.
The aim of this study is to examine whether pregnancy is associated with morphological brain changes in women. In this longitudinal case-control study, we obtained high-resolution brain MRI scans of 25 primiparous women and their male partners (n=19) before and after pregnancy. Longitudinal scans of 20 nulliparous control women and their male partners (n=17) were also acquired. A longitudinal voxel based morphometric analysis was applied to calculate changes in grey matter (GM) between the two different time-points and compare these changes between the groups of subjects (primiparous versus controls).
Group comparisons of these within-subject GM changes indicate a symmetrical pattern of highly significant GM volumetric reductions in the women who underwent pregnancy in comparison to the nulliparous control women. The comparison between the male samples does not yield significant differences.
These GM volume reductions associated with pregnancy are observed in the posterior midline (posterior cingulate and precuneus), the medial frontal cortex (medial prefrontal cortex and anterior cingulate), bilateral lateral prefrontal cortex (clusters in the ventrolateral and dorsolateral prefrontal cortex) and bilateral temporal cortex (bilateral superior temporal sulcus extending to surrounding lateral temporal sections as well as medial temporal structures such as the fusiform gyrus). All p values are below 0.05 familywise-error corrected.
The changes are remarkably consistent across subjects and the women can significantly be classified as having undergone pregnancy or not, based on the distribution of GM changes across the brain.
The current findings are the first to demonstrate that pregnancy is related to specific morphological brain changes in humans, providing primary insights into the way a woman’s brain is modified during pregnancy.
The results are discussed in the light of studies assessing the implicated brain areas and the potential neurobiological mechanisms underlying these GM volume reductions. Although the mechanism and physiological meaning of these findings are speculative at the present time, these findings provide primary clues regarding the neural basis of motherhood, perinatal mental health and brain plasticity in general.